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3 Answers
3

It is apparently not safe, among the poor today who have to use it as they have no alternatives, it leads to all sorts of health problems.
It is also a worse polutant than burning wood.

On the reverse side of the environmental equation, raw biomass is known to emit a number of particulates as well as polycyclic aromatic hydrocarbons (PAHs). Burning solid biomass directly contributes to reduction in air quality, often to a greater degree than oil or other hydrocarbons. Burning animal waste creates more dioxin and chlorophenol pollutants than burning wood does. This is particularly harmful when it is burned indoors without venting.

PAHs are well-known carcinogens having the potential to damage DNA and cause birth defects. Dioxins are derivatives of PAHs and are known to be highly toxic to fish and wildlife. A dioxin level as low as 0.5 micrograms/kilogram (about 0.0000005% by mass) are lethal to some species. Chlorophenol is also an aromatic compound. It is commonly used in pesticides, herbicides, and disinfectants. It is one of the primary components of mothballs. Chlorophenol is less toxic than the above compounds, with lethal doses in the range of 600 milligrams/kilogram or about 50% by mass. Long-term exposure to relatively high levels can lead to damage to red blood cells and to the immune system.

The burning of biomass in the developing world for heating and cooking results in high indoor particle concentrations. Long-term exposure to airborne particulate matter (PM) has been associated with increased rates of acute respiratory infections, chronic obstructive lung disease and cancer.

According to health experts, the smoke released in the burning process contains hazardous gases. Studies show that by inhaling these, people suffer from diseases. There are specially made chulhas or stoves for using of dung cakes. Usually these cakes consist of groundnut husk; paddy straw is also used. When the cakes are burnt, dangerous gases are released, which is then inhaled by people. .

The study by Jadavpur University's School of Environmental Studies says the region's groundwater is contaminated with the cancer-causing chemical which gets into paddy through contaminated water. Cattle that feed on contaminated paddy husk and water produce dung that is likely to contain arsenic.

Researchers say while the dung is burnt in kitchen, as much as 25 per cent of the arsenic in fumes could be absorbed by the respiratory tract of people and lead to diseases such as persistent cough and chronic bronchitis. The arsenic particles in the air might also settle on food and water and contaminate it.

Note

In 2010 there was an effort to create and distribute better stoves to avoid these problems but while better, it seems that they still had safety problems.

But “clean” is a nebulous term. Of those 28 million cookstoves, only 8.2 million — the ones that run on electricity or burn liquid fuels including liquefied petroleum gas (LPG), ethanol and biogas — meet the health guidelines for indoor emissions set by the WHO. The vast majority of the stoves burn wood, charcoal, animal dung or agricultural waste — and aren’t, therefore, nearly as healthy as promised. Although these cookstoves produce fewer emissions than open fires, burning biomass fuels in them still releases plenty of toxins. “As yet, no biomass stove in the world is clean enough to be truly health protective in household use,” says Kirk Smith, a professor of global environmental health at the University of California at Berkeley and the leading health researcher on cookstoves

Note that the last issue (arsenic poisoning) is peculiar to Bangladesh. Bangladesh has very high, but naturally occurring, levels of arsenic in it's sub-soils and bedrock. Deep tube wells are dug for water, but the wells pass through layers of soil and rock that contain lots of arsenic, leaving the water, and the irrigated fields contaminated with high levels of arsenic. Then when cows eat the grass from the contaminated fields their feces become contaminated too.
– Charles E. GrantDec 10 '18 at 20:26

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The first two quotes seem to imply indoor use... I'm wondering if you found anything that suggests, for example, an outdoor fire pit.
– RofloDec 10 '18 at 21:28

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@Roflo The only people who use it have no choice, which seems to suggest that if you have a choice, you should use something else
– Charlie BrumbaughDec 10 '18 at 21:39

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+1 but I wonder: people who are burning dung for fuel are poor and probably have inefficient stoves. Wood burns cleaner in a more efficient stove. What would happen if we burnt dung in something like a rocket stove?
– Chris HDec 10 '18 at 22:03

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its important to read the sources rather than the quotes - this is a very misleading answer. The toxicity of these agents are vastly overstated although if you read the article the numbers are correct (yes ingesting a mass of 50% of your total body weight of just about anything is probably toxic, and I am sure that there are some gnats that for which .0000005% - yup that's 7 zeros-) worth of a toxin will in fact be toxic.
– Jim BDec 11 '18 at 14:41

Smoke has it's hazards. For 30 years I cooked over open fires for about 6 weeks a year. It's irritating as heck, but I don't have obvious problems. That may be about as good as the 2 pack a day smoker at age 65 saying, "Hasn't kilt me yet"

Burning any form of biomass works better if the material is dry. Damp material uses a lot of energy to evaporate water. The resulting lower temperatures make for incomplete combustion.

ANY form of stove can improve the situation by creating some form of focused draft. A chimney can move the smoke far enough away from the cook to reduce his exposure by orders of magnitude.

In the settling of the American west, cow chips and road apples (horse...) were used for cooking as there was little else to burn. Collecting this stuff was a job for kids. Stuff that wasn't dry, but was solid enough to pick up could be put in a canvas slung under the wagon to dry. You find similar use by aboriginal tribes that lived on plains or steppes.

Depending on what you are collecting and where, there may be risk of parasite transfer. I don't know that the tape worm that infects cows also infects people, but I'd expect it to. There are doubtless bacteria in meadow muffins that will leave you unhappy too.

Off the top of my head I would consider this aspect to be the higher hazard.

Dried cattle dung is somewhat safer than wood in so far as it produces fewer sparks and therefore is less likely to set the surroundings on fire. This is especially important if you have an open fire inside a dwelling, e.g. in Mongolian yurts before the 20th century. Nowadays yurts always have an iron stove, so this is less of a concern. But people in the countryside still burn dried cattle dung ("argal" in Mongolian) because it is often easier accessible than firewood.

Argal is actually somewhat associated with healthy country life, sung about in songs, and was even used by the Great Khans in the past:

The house was all covered inside with cloth of gold, and there was a fire of briars and wormwood roots--which grow here to great size--and of cattle dung, in a grate in the center of the dwelling.